Control of electrically efficient led arrays

ABSTRACT

An LED lamp comprising: a plurality of LED strings, each LED string comprising a plurality of LEDs; a plurality of constant current circuits for powering the plurality of LED strings, wherein one constant current circuit is provided for each LED string; a plurality of shift registers for controlling the operation of the plurality of constant current circuits, wherein at least one shift register is provided for each LED string; and a microprocessor for supplying timing pulses to the plurality of shift registers for controlling operation of the plurality of constant current circuits, the timing pulses comprising a plurality of serial bit streams.

REFERENCE TO PENDING PRIOR PATENT APPLICATION

This patent application claims benefit of pending prior U.S. ProvisionalPatent Application Ser. No. 62/251,332, filed Nov. 5, 2015 byProPhotonix Limited and Peter Panek et al. for CONTROL OF ELECTRICALLYEFFICIENT LED ARRAYS (Attorney's Docket No. PROPHOTONIX-4 PROV), whichpatent application is hereby incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to lighting devices in general, and moreparticularly to a modular LED lamp (e.g., a backlight) and acurrent-regulating drive circuit for LED strobe operation that cancontrol individual elements of the LED arrays of the lamp (e.g., thebacklight).

BACKGROUND OF THE INVENTION

Machine vision is the technology used to provide imaging-based automaticinspection and analysis for applications such as parts inspection,process control, and robot guidance in industry. Employing the correctlighting is critical to creating a reliable, repeatable machine visionapplication.

Currently, the light sources commonly applied in machine visioninspection systems include halogen-, fluorescence-, xenon-, LED- andOLED-based lamps. Since the LED has many advantages over other lightsources (such as long lifetime, low power consumption, fast responsetime, low probability of damage, etc.), the LED has been widely adoptedin machine vision inspection systems and has gradually replaced otherlight sources to become the most commonly utilized technology in themarket.

Lamps are available in various form factors including area, line, ringand spot lamps. Lamps provide lighting which is often used in machinevision systems for inspecting objects, e.g., to provide a backlight forilluminating an object to be inspected from behind the object (relativeto a camera or imager). Such backlights allow features of the objectwhich is to be inspected, especially peripheral features, to be observedmore clearly than when the object is illuminated directly (i.e., fromthe front of the object). By way of example but not limitation, thepresent invention comprises the provision and use of an electronicengine for an LED backlight. However, it will be appreciated by thoseskilled in the art that the present invention can also be utilized inother types of lights (e.g., direct light lamps) and in a variety ofform factors.

Machine vision systems can only generate high quality images if thelighting used to inspect an object clearly defines the elements of theobject which is being inspected. For many applications, the object underinspection is moving at high speed past the camera and lightingapparatus, and/or a high intensity light is required in order to achievea meaningful measurement of the object being inspected. In thesesituations, the LED lights are often overdriven by strobe (or pulse)control so as to increase the intensity from the LED light source for ashort, defined period of time. This is to ensure successful imagecapture by the camera system. This requirement for strobe (or pulse)control can add complexity to the design of the LED control circuitrywhen large numbers of LEDs are required.

In addition, in machine vision, it is sometimes desirable to change theLED pattern profile while strobing as a means to further inspect items.In other words, it is sometimes desirable to select which LEDs will bepowered so as to form a desired form factor (e.g., an area lamp, a linelamp, a ring lamp, a spot lamp, etc.). This requires that the user havethe ability to individually control the various LEDs used in the lamp,which can further increase the complexity and cost of the LED controlcircuitry. It is also often desirable to be able to create and storepatterns of LED activation for future use, and not be reliant on“factory set” patterns of LED activation. This can be important where acustom-designed LED activation pattern is required by the user.

1. Issues with Large LED Arrays

There is an increasing demand for higher intensity (i.e., brighter),LED-based lamps (e.g., backlights) for use with high speed inspection ofa variety of products and materials. This demand has led to thedevelopment of large LED array systems comprising hundreds (or eventhousands) of individual LEDs. Currently-available LED array systems aretypically limited by a variety of issues. By way of example but notlimitation, currently-available LED array systems typically cannotaddress individual LEDs within the large LED arrays, are generally quitelarge and bulky, are typically complex, are typically inefficient,generally require large power supply units (e.g., in excess of onekilowatt) and are typically very expensive.

In these large LED array systems, the LEDs are typically placed in aseries, or in parallel strings, which limits the controllability toindividual strings (or “boards”) of LEDs. When LEDs are connected inseries, brightness-matching is typically maximized, meaning that thevariation of brightness of one LED in the series compared to another LEDin the series is not visible. The primary disadvantage of using a seriesconfiguration is that the output voltages can be very high when largenumbers of LEDs are used. Connecting strings of LEDs in parallel willtypically reduce the maximum string voltage required, and will also addsome fault immunity. However, the disadvantages of using a parallelconfiguration are power consumption in the balance resistors,non-uniformity of the optical output and lower system efficiency.

There are numerous strategies that can reduce the aforementioned issues,such as matrix-type configurations, but all of these strategiesultimately lead to increases in the size and cost of the LED arraysystem. Furthermore, many of these strategies are inefficient, inasmuchas they draw electrical power even when it is not required, by virtue ofbeing powered continuously. LED array systems that use strobingtechniques to reduce the continuous power draw typically require largeand expensive power supply units (e.g., >1 kilowatt). This in turnrequires the use of expensive (and large gauge) wiring and cabling whichlimits the flexibility and modularity of the overall LED array system.

Some manufacturers use microcontrollers in the LED array systems inorder to manage individual constant current drivers for the LEDs.However, for systems with a large number of LEDs, a singlemicrocontroller is not able to balance the LED currents to the precisionthat is generally required. Adding a microcontroller for each LED string(i.e., for each group of LEDs) generally leads to an unacceptable risein costs and an increase in the space required for the LED controlcircuitry.

Pulse Width Modulation (PWM) is a standard technique for controlling theintensity of light pulses. Instead of increasing or decreasing thebrightness of the light by varying the current to the LEDs, the light israpidly switched on and off in a regular pattern. The intensity of thelight is governed by the duty cycle, by varying the proportions of thetime that the light is on or off. Maximum intensity (i.e., brightness)is achieved when the light is on 100% of the time, 50% brightness isachieved when the light is on for half the time, etc.

PWM control circuitry is typically created using specialty hardware inan embedded microcontroller unit (MCU). Most MCUs have one or morehardware PWM outputs for such applications. However, for large scale LEDarrays, these techniques are not suitable. For example, if an LED arraysystem had 1000 LEDs, each LED would need to be individually controlledby the MCU. Therefore this system would need approximately 1000separately-controlled PWM outputs for the MCU. PWM can also be effectedin software in a loop, turning the light on for a timed period and thenturning it off for a timed period. However, in software implementations,the MCU is limited by clock speed and other factors. Therefore, only arelatively small number of PWM outputs can be implemented using softwareimplementations before the limits of the MCU are reached.

Therefore, it would be desirable to provide a modular LED driving andcontrol scheme that can address individual elements of a large array ofLEDs at a reasonable cost and which is easily scalable, flexible indesign so as to allow for various form factors, and which worksindependently of device wavelength, device type (e.g., LED, OLED, etc.)0L system power requirements, while still allowing the user full controlof various strobe profile parameters.

SUMMARY OF THE INVENTION

The present invention comprises the provision and use of a modular LEDlamp (e.g., backlight), and more particularly a modular LED lamp (e.g.,backlight) comprising a current-regulating drive circuit for an LEDstrobe drive that can control the individual LEDs of the LED array. Theinvention uses one central processor which connects via shift registerarrays to address each LED in a panel or series of panels. During theLED off-time, a pulse energy charging system is used to minimize thetotal input current required by the system during operation (i.e.,during the LED on-time).

The system is fully modular and flexible. Various types of LEDs, orsimilar light sources, can be accommodated by the present inventionwithout modifying the system hardware. In order to control the largenumber of LEDs, complex software structures, based on saturatedmathematics, are utilized. For the remainder of this disclosure, onlyLED-based systems will be discussed. However, it will be apparent tothose skilled in the art that the present invention can be utilized inconjunction with other light sources such as OLEDs, SLEDS, etc.

In one preferred form of the invention, there is provided an LED lampcomprising:

a plurality of LED strings, each LED string comprising a plurality ofLEDs;

a plurality of constant current circuits for powering the plurality ofLED strings, wherein one constant current circuit is provided for eachLED string;

a plurality of shift registers for controlling the operation of theplurality of constant current circuits, wherein at least one shiftregister is provided for each LED string; and

a microprocessor for supplying timing pulses to the plurality of shiftregisters for controlling operation of the plurality of constant currentcircuits, the timing pulses comprising a plurality of serial bitstreams.

In another preferred form of the invention, there is provided a novelmethod for producing light, the novel method comprising:

providing an LED lamp comprising:

-   -   a plurality of LED strings, each LED string comprising a        plurality of LEDs;    -   a plurality of constant current circuits for powering the        plurality of LED strings, wherein one constant current circuit        is provided for each LED string;    -   a plurality of shift registers for controlling the operation of        the plurality of constant current circuits, wherein at least one        shift register is provided for each LED string; and    -   a microprocessor for supplying timing pulses to the plurality of        shift registers for controlling operation of the plurality of        constant current circuits, the timing pulses comprising a        plurality of serial bit streams; and

causing the microprocessor to supply appropriate timing pulses toappropriate ones of the plurality of shift registers so as to activateselected ones of the plurality of LEDs on the plurality of LED strings.

In another preferred form of the invention, there is provided a lampcomprising:

a plurality of lighting strings, each lighting string comprising aplurality of light sources;

a plurality of powering circuits for powering the plurality of lightingstrings, wherein one powering circuit is provided for each lightingstring;

a plurality of shift registers for controlling the operation of theplurality of powering circuits, wherein at least one shift register isprovided for each lighting string; and

a microprocessor for supplying timing pulses to the plurality of shiftregisters for controlling operation of the plurality of poweringcircuits, the timing pulses comprising a plurality of serial bitstreams.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects and features of the present invention will bemore fully disclosed or rendered obvious by the following detaileddescription of the preferred embodiments of the invention, which is tobe considered together with the accompanying drawings wherein likenumbers refer to like parts, and further wherein:

FIG. 1 is a block diagram of the LED lamp (e.g., backlight) electronicsused in connection with the present invention;

FIG. 2 is a block diagram of the LED array electronics utilizing one LEDpanel;

FIG. 3A is a block diagram of the microprocessor control of an LEDstring using a 16-bit constant current driver integrated circuit;

FIG. 3B is a schematic view showing timing pulses transferred from themicroprocessor to the shift registers as a plurality of serial bitstreams;

FIGS. 4A and 4B are schematic views showing SISD and SIMD architectures,respectively;

FIG. 5 is a schematic view showing a PWM algorithm;

FIG. 6A is a schematic view showing serial shift register connections;

FIG. 6B is a schematic view showing parallel shift register connections;

FIG. 7 is a schematic view showing a switcher circuit for optimizing thevoltage required for an LED string; and

FIGS. 8A-8D are schematic views showing a monochromatic LED panel withexemplary programmable patterns.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The LED Lamp (e.g.,Backlight) in General

The present invention provides a series of design innovations toovercome issues with the prior art. This disclosure will primarilydiscuss the invention in the context of a monochromatic LED backlightconfiguration. However, it will be appreciated by those skilled in theart that the present invention can be applied to any LED arrayconfiguration, e.g., a line light, a ring light, etc. Furthermore,various types of LEDs can be accommodated with the present invention.For example, monochromatic, infrared or ultra-violet (UV) light sourcescan all be utilized without the need for any changes to the circuithardware or infrastructure. LED forward voltages, drive currents, pulsewidths, durations, etc. are all controlled by software.

As shown in FIG. 1, a backlight 5 formed in accordance with the presentinvention may comprise seven basic elements: a GUI interface 10, a DCpower supply 15, a processor printed circuit board (PCB) 20, a boostcharge converter PCB 25, a switcher PCB 30 (which includes a capacitorbank, see below), and an LED panel PCB 35 which is driven by integratedcircuits (ICs) 40. Backlight 5 can include multiple LED panels 35. Itwill be appreciated by those skilled in the art that the number of LEDspopulating each LED panel 35, and the number of LED panels 35 includedin backlight 5, can be easily scaled with the design methodology used inthe present invention. For clarity of illustration, the followingdisclosure will describe in more detail a backlight 5 where only one LEDpanel 35 is utilized.

FIG. 2 shows further details of an exemplary backlight 5 comprising asingle LED panel 35. Backlight 5 is powered by DC power supply 15, forexample, a 48V power supply. Custom GUI interface 10 allows the user tocontrol the backlight via an Ethernet connection 45 to themicroprocessor 50 located on processor PCB 20. Processor PCB 20comprises microprocessor 50, Ethernet electronics 45 and one or moretrigger circuits 55. Trigger circuits 55 allow strobe light pulses to besynchronized to the machine vision capture system. Trigger schemes canalso include direct strobe time period control or user-defined LEDdisplay patterns with set intensities and timings.

Microprocessor Control of Each Individual LED

Microprocessor 50 provides full control of IC(s) 40, which mainlycomprise shift registers (SRs) and constant current (CC) drivers (seebelow). Microprocessor 50 connects to, and addresses, every individualLED in LED panel 35 via these shift registers. A single signal (via abit stream) can be sent from microprocessor 50 into ICs 40 to controlmultiple LEDs on LED panel 35 (or to control the LEDs on multiple LEDpanels 35, where multiple LED panels are utilized in backlight 5).

On receiving instructions from GUI interface 10, microprocessor 50communicates with both IC PCB 40 and switcher PCB 30. First, the strobeprofile for LED panel 35 is transferred from microprocessor 50 into theshift registers located on IC PCB 40. LED timing pulses are generatedfrom microprocessor 50 as a number of serial bit streams. A typical bitstream profile of an LED string 60 of 16 LEDs is shown in FIGS. 3A and3B. Microprocessor 50 sends a series of hit streams, one at a time, to a16-bit shift register 65. Once a bit stream has been fully loaded intoshift register 65, the instructions are sent to constant current drivers70 and the ON or OFF signals are sent out to the 16 LEDs in LED string60.

The number of bit streams sent from microprocessor 50 to shift registers65 per millisecond (ms) is determined by the size of microprocessor 50.Using an 8-bit microprocessor 50, a total of 256 (i.e., 2⁸) steps can betransferred per millisecond. Using a 10-bit microprocessor 50, a totalof 1024 (i.e., 2¹⁶) steps can be transferred per millisecond.

Assume that the user requires a strobe time of 1 ms. A total of 25616-bit streams can be sent by microprocessor 50 to the LEDs in LEDstrings 60 via shift registers 65 within 1 ms. The camera of the machinevision system integrates all 256 steps for that 1 ms, and it is thisintegration of 256 steps that makes up the strobe profile. Even thoughthe LEDs in LED strings 60 have only two settings (i.e., ON or OFF), theintegration by the camera allows for variation in brightness, so thepower of each LED is selectable in 255 steps, from 1 (dimmest setting)to 255 (brightest setting). Therefore, the pulse duration can becontrolled so as to allow the user to adjust the amount of lightintegrated by a camera in a machine vision system. The variations in theamount of light generated are achieved by varying the on-time of theLEDs across the 256 steps. In other words, the variations in the amountof light generated by an LED are controlled using a PWM scheme.

By way of example but not limitation, and looking now at FIG. 3B, the 1ms strobe profile is constructed from 256 separate 16-bit streams whereeach ON time is 3.9 μs long (1 ms/256). As shown in FIG. 3B, for thefirst 64 steps, the first 12 LEDs in LED string 60 are turned ON and theremaining LEDs in LED string 60 are left OFF. For the next 64 steps(i.e., steps 65-128), the first 8 LEDs in LED string 60 are turned ONand the remaining LEDs in LED string 60 are left OFF. For the next 64steps (i.e., steps 129-192), the first 4 LEDs in LED string 60 areturned ON and the remaining LEDs in LED string 60 are left OFF. For thefinal 64 steps (i.e., steps 193-256), the first 2 LEDs in LED string 60are turned ON and the remaining LEDs in LED string 60 are left OFF. Theresulting 1 ms strobe profile, following camera integration, is avariation in LED brightness from full brightness to minimum brightnessfrom LED 01 to LED 16. It will be appreciated by those skilled in theart that any configuration may be possible using this scheme.

SIMD Processor and Saturated Arithmetic

For an application that requires 1000 LEDs which must be controlledusing a PWM scheme with only one transition, each LED is turned on onceand turned off once per cycle. The length of time that the LED is “on”is adjusted so as to give the required intensity for each LED. Theoverall strobe length may be up to 1 ms, and 256 levels of intensity areavailable per LED. This means that each LED may be turned on or off atany 3.9 μs interval. The number of PWM calculations per second istherefore:

(1/3.9×10⁻⁶)×1000=256,410,256

For a small MCU (e.g., microprocessor 50) with a 200 MHz clock rate,this is too many calculations to do using standard instructions. By wayof example but not limitation, peak performance of this MCU is about 1operation per clock cycle but each PWM calculation requires at least 8instructions. Each calculation must read a PWM value, compare it to atime interval and then write the correct value out to the LED output.This means that normal instructions and arithmetic will not suffice fora small microprocessor with this 1000 LED array example.

To this end, the present invention combines a Single Instruction,Multiple Data stream (SIMD) processor and saturated arithmetic toproduce a software algorithm which can calculate the 1000 PWM outputs(for the 1000 LEDs in the example) with sub-microsecond precision.

More particularly, and looking now at FIG. 4A, it will be seen that aSingle Instruction, Single Data stream (SISD) processor is a sequentialcomputer which exploits no parallelism in either the instruction or datastreams. A single control unit fetches a single instruction stream frommemory. The control unit then generates appropriate control signals todirect the single processing element to operate on a single data stream(i.e., one operation at a time) and outputs the result.

In contrast, and looking now at FIG. 4B, a Single Instruction, MultipleData stream (SIMD) processor runs the exact same program (that is, the“single instruction” part of the program) on each of itssimultaneously-executing parallel units. For example, the ARM Cortex-M4processor has SIMD instructions which can do up to four arithmeticcalculations in one instruction. These SIMD processors are managed usingarithmetical operations. Typically, an eight-bit byte can be used tostore the values from 0 to 255. With normal arithmetic, adding 1 to themaximum value 255 causes the register to “wrap around” back to 0.Subtracting 1 from 0 causes the register to wrap around back to 255.

An alternative technique is to use saturated arithmetic where there isno “wrap around”, i.e., adding two values whose sum exceeds 255 willstill yield 255 inasmuch as this is the maximum value allowed (wherethere is no “wrap around”). The register is said to be “saturated” to255. Similarly, subtracting a larger value from a smaller value will besaturated to zero (since this is the minimum value allowed where thereis no “wrap around” with the register). In essence, when using saturatedarithmetic, there is no wrap around for the register.

With the present invention, an SIMD processor and saturated arithmeticare combined (i.e., microprocessor 50 comprises an SIMD processorprogrammed to use saturated arithmetic in its internal registers) toproduce a software algorithm which can calculate 1000 PWM outputs (forthe 1000 LEDs in the example) with sub-microsecond precision. Each PWMoutput is controlled by an 8-bit register value. The PWM value is alwaysodd. Every cycle, bit 0 of the PWM register is written to a single LED.This means that if the register value is odd, the light is on, and ifthe register value is even, the light is off.

At each cycle, 2 is subtracted from the PWM register. When the PWM valuereaches 1, the next subtraction will make the register zero and, whenthis is written to the LED, the light is turned off (because if theregister value is 0, the light is off).

Alternatively, to save storing a new value to the PWM register aftereach subtraction, on each cycle, a counter value is subtracted from eachPWM register. This counter value (i.e., the value subtracted from eachPWM register on each cycle) is incremented by 2 on each cycle. When thecounter value is greater than the PWM register, the output (i.e., theresultant of the counter value being subtracted from the PWM register)is zero. On all other cycles prior to this one, the output (i.e., theresultant of the counter value being subtracted from the PWM register)is an odd integer. The least significant bit of the output (i.e., theresultant of the counter value being subtracted from the PWM register)indicates whether the output value is odd or even. It is this outputvalue which is written to the General Purpose Input/Output (GPIO)register for microprocessor 50 (see below) to turn the LED on or off.

The SIMD processor (i.e., microprocessor 50) uses the SIMD instructionsto do four of these calculations in one operation. In addition, theinstructions are carefully arranged so that they pipeline theirdifferent phases, allowing microprocessor 50 to do four PWM operationsin one clock cycle. The PWM algorithm is shown in FIG. 5. As seen inFIG. 5, 4 bytes of PWM data (labelled N_(i) to N_(i+3)) are fed into asaturated subtraction operation where X_(t) is subtracted and the resultO_(i) to O_(i+3) used to drive General Purpose Input/Output (GPIO)signals (a generic pin on microprocessor 50) on bit 0 of the result ofeach subtraction. One operation therefore delivers four bits of theserial stream simultaneously. These results are fed out onto GPIOsfeeding serial streams S_(m) to S_(m+3). These serial streams drive theLEDS via shift registers 65.

Integrated Circuits 40

For lamps (e.g., backlights) where large numbers of LEDs are used, anumber of strategies (e.g., the use of larger shift registers, the useof serial shift register connections or the use of parallel shiftregister connections) may be used to manage LED profiles. See FIGS. 6Aand 6B. The choice of strategy to use will depend primarily on therequirements for intensity levels and the allowable time betweenindividual strobes. More particularly, assume that an LED string 60contains 26 LEDs in series. An IC 40 with a 16-bit shift register 65will only hold the profiles of 16 LEDs, leaving the profiles of 10 LEDswith nowhere to be stored.

One solution is to use an IC 40 with a larger bit shift register 65,i.e., d 32-bit shift register. However, inputting a shift register withmore bits means an increase in the time to input the bit stream into theshift register. This means that the required time between strobe flashesincreases.

A second solution is to use two IC's 40 connected together where thefirst 16 LED profiles are stored in the first integrated circuit (IC1)40 and the final 10 LED profiles are stored in the second integratedcircuit (IC2) 40, as shown in FIG. 6A. Note that in this instance, thebit stream entering IC1 40 is a single bit stream from a singlemicroprocessor channel containing the profiles for all 26 LEDs. Again,the required time between strobe flashes increases.

Another solution is to use, again, multiple ICs 40, but in this instancethe bit streams are split up and leave microprocessor 50 from separatechannels. See FIG. 6B. For example, the first channel might send a16-bit stream and the second channel might send a 10-bit stream. In thisinstance, the time between strobes is optimized by sending the LEDprofile bit stream via two channels from microprocessor 50 to two ICs 40(i.e., IC1 and IC2). Utilizing all the available channels inmicroprocessor 50 and multiple shift registers 65 in multiple ICs 40allows the user to control a large number of LEDs without requiring anincrease in the time between strobe flashes. For example, if a 24-bit“deep” shift register 65 is used in conjunction with microprocessor 50having 32 parallel outputs, then 768 individual LEDs (i.e., the productof 24×32) can be controlled by the microprocessor output.

For individual LEDs, microprocessor 50 can turn on or off the LEDs atvarious intensities, pulse duty cycles, voltages and currents via outputcontrol signals. Pulse delays can also be programmed if required.Microprocessor 50 can define the pattern from which individual ormultiple LEDs are turned on or off. Multiple LED light strobe profilescan be programmed and stored locally (i.e., in the lamp). The systemalso allows for a particular LED array pattern to be changed inreal-time while the system is connected to a camera and a test unit.

Once the entire bit stream profile has been stored in the shiftregister(s) 65, these pulses are then latched into multiple channel LEDconstant current drivers 70. Constant current drivers 70 are effectivelyused as shift registers, the depth of which is usually the same as shiftregisters 65 (i.e., a 16-bit shift register 65 may be paired with a16-bit constant current driver 70). Constant current drivers 70 maintainthe LED current at a set level. This allows the LED to emit light of thesame intensity within the LED bin specification. The LED current can bedefined by hardware configuration or via software control. This allowsthe LEDs to emit light of the same intensity (i.e., brightness) withinthe LED bin specification.

Switcher PCB 30

At the same time that microprocessor 50 is communicating with IC's 40,it is communicating with switcher PCB 30 (of which the microprocessorhas full control). Switcher PCB 30 provides power to an LED panel 35. AnLED panel 35 consists of numerous LED strings 60. Switcher PCB 30 can bemade up of numerous switcher circuits 75 where each switcher circuit 75corresponds to an LED string 60. Microprocessor 50 can turn on or offany or all of switcher circuits 75 through a dedicated enable signal.Switcher PCB 30 provides full control of a series of switcher circuits75 depending on the number of LED strings 60 on LED panel 35—oneswitcher circuit 75 is provided for each LED string 60.

Switcher PCB 30 also sets the optimum constant current driver workingvoltage.

Properly powering a light emitting diode (LED) or group of LEDs (e.g.,an LED string 60) is different than powering most electronics. Whilemost electronics require a constant voltage source, LEDs require aconstant current source. With the large number of LEDs on a backlight, ahigh instantaneous LED current (e.g., at least 100 A) is required toensure that all LEDs operate at their maximum intensity when a pulse isapplied. Prior art systems have maintained an “always ready” direct LEDpower supply which requires the use of expensive high power Power SupplyUnits (PSUs).

In contrast, the present invention provides a novel means for reducingthis power requirement while maintaining precision control of the outputcurrent driving the LEDs. With the present invention, the LEDs arestrobed ON for short time periods. In order to reduce power consumption,and system cost, a pulse energy storage system is utilized via a boostconverter circuit (i.e., the aforementioned boost charge converter 25).For the backlight example utilizing a 48V power supply, while the LEDsare off, this pulse energy storage system takes the inputted voltage andcurrent and charges a bank of electrolytic capacitors 80 from 0V to 60V.A series of switcher circuits 75 then takes the variable voltage chargefrom capacitors 80 and converts it to a constant voltage which can beapplied to the LEDs. This charge is sufficient to strobe the LEDsseveral times.

In the example shown in FIG. 7, a switcher circuit 75 is used tooptimize the required voltage for an LED string 60 consisting of, inthis example, two LEDs 85. Each LED 85 draws down 3.34V volts. It isknown that IC 40 draws approximately 1V. Adding this together gives atotal voltage requirement for LED string 60 of 7.68V, i.e.,((3.34V×2)+1V)=7.68V. Adding some redundancy, an optimum voltage for LEDstring 60 to draw down would be 8V. Switcher circuit 75 can becontrolled to draw down, when required, 8V from boost charger circuit 75and transfer the appropriate current to LED string 60.

These features greatly reduce the overall system current requirement,for example, from 100 A to as low as 3 or 4 A. This allows for asignificant system cost reduction as smaller and cheaper wiring can thenbe utilized and much smaller power supply units (PSUs) are required.This leads to a much smaller and cost efficient system. This moreoptimized system can now be reduced to a series of interconnectingmodules leading to cost savings in manufacturing and on-goingmaintenance.

Modular Design

In a further embodiment of the present invention, the entire system canbe designed to be modular. For this particular backlight, LED panel 35comprises seven LED strips 60 of 204 LEDs each. See FIGS. 8A, 8B, 8C and8D for an exemplary LED panel 35 with exemplary programmable patterns.Each and every LED strip 60 in LED panel 65 is removable andreplaceable. Each switcher board 30 comprises seven switcher circuits75, one switcher circuit 75 per LED strip 60. All switcher boards 30 areremovable and replaceable. All PCBs connect neatly to each other usingheaders which eliminate the need for cabling or soldering. Should anycomponent fail or require replacement, it is a simple task to remove andreplace a board.

SOME ASPECTS OF THE PRESENT INVENTION

Thus it will be seen that the present invention provides a number ofnovel features, including but not limited to:

1. the unique software feature of this invention implements a largenumber of PWM outputs in software which is significantly lower in costand more general than the usual hardware solution;

2. a single processor is used to control hundreds of pixels and can bescaled to several thousand; and

3. a unique amalgamation of technologies is used—individual pixeladdressing with serial shift registers, constant current drivers withhigh current LEDs, a single management processor, a charger withcapacitor bank and strobe circuitry.

MODIFICATIONS OF THE PREFERRED EMBODIMENTS

It should be understood that many additional changes in the details,materials, steps and arrangements of parts, which have been hereindescribed and illustrated in order to explain the nature of the presentinvention, may be made by those skilled in the art while still remainingwithin the principles and scope of the invention.

What is claimed is:
 1. An LED lamp comprising: a plurality of LEDstrings, each LED string comprising a plurality of LEDs; a plurality ofconstant current circuits for powering the plurality of LED strings,wherein one constant current circuit is provided for each LED string; aplurality of shift registers for controlling the operation of theplurality of constant current circuits, wherein at least one shiftregister is provided for each LED string; and a microprocessor forsupplying timing pulses to the plurality of shift registers forcontrolling operation of the plurality of constant current circuits, thetiming pulses comprising a plurality of serial bit streams.
 2. An LEDlamp according to claim 1 wherein the microprocessor is configured tocontrol the intensity of each of the plurality of LEDs in the pluralityof LED strings by varying the timing pulses sent to the plurality ofshift registers.
 3. An LED lamp according to claim 2 wherein themicroprocessor is configured to control the intensity of each of theplurality of LEDs in the plurality of LED strings using Pulse WidthModulation (PWM).
 4. An LED lamp according to claim 1 wherein themicroprocessor comprises a Single Instruction, Multiple Data stream(SIMD) processor.
 5. An LED lamp according to claim 4 wherein themicroprocessor uses saturated arithmetic.
 6. An LED lamp according toclaim 1 wherein the at least one shift register provided for each LEDstring comprises a single shift register.
 7. An LED lamp according toclaim 1 wherein the at least one shift register provided for each LEDstring comprises a plurality of shift registers configured in series anddriven by a single output channel of the microprocessor.
 8. An LED lampaccording to claim 1 wherein the at least one shift register providedfor each LED string comprises a plurality of shift registers configuredin parallel and driven by a plurality of output channels of themicroprocessor.
 9. An LED lamp according to claim 1 further comprising apower supply and a plurality of switcher circuits, wherein one switchercircuit is provided for each LED string, and further wherein themicroprocessor controls the plurality of switcher circuits to regulatethe delivery of power to the plurality of LED strings.
 10. An LED lampaccording to claim 9 further comprising at least one capacitor forreceiving power from the power supply and providing power to theplurality of switcher circuits.
 11. An LED lamp according to claim 1wherein the microprocessor is pre-programmed so as to supply appropriatetiming pulses to appropriate ones of the plurality of shift registers soas to activate selected ones of the plurality of LEDs on the pluralityof LED strings.
 12. An LED lamp according to claim 1 further comprisinga Graphical User Interface (GUI) communicating with the microprocessorfor enabling a user to instruct the microprocessor so as to supplyappropriate timing pulses to appropriate ones of the plurality of shiftregisters so as to activate selected ones of the plurality of LEDs onthe plurality of LED strings.
 13. An LED lamp according to claim 1further comprising at least one trigger circuit communicating with themicroprocessor.
 14. An LED lamp according to claim 13 wherein the atleast one trigger circuit communicates with a machine vision inspectionsystem so as to coordinate operation of the LED lamp with the machinevision inspection system.
 15. An LED lamp according to claim 1 furthercomprising a panel, wherein a plurality of LED strings are independentlymounted to the panel such that one LED string may be removed from thepanel without effecting operation of the remaining LED strings mountedto the panel.
 16. A novel method for producing light, the novel methodcomprising: providing an LED lamp comprising: a plurality of LEDstrings, each LED string comprising a plurality of LEDs; a plurality ofconstant current circuits for powering the plurality of LED strings,wherein one constant current circuit is provided for each LED string; aplurality of shift registers for controlling the operation of theplurality of constant current circuits, wherein at least one shiftregister is provided for each LED string; and a microprocessor forsupplying timing pulses to the plurality of shift registers forcontrolling operation of the plurality of constant current circuits, thetiming pulses comprising a plurality of serial bit streams; and causingthe microprocessor to supply appropriate timing pulses to appropriateones of the plurality of shift registers so as to activate selected onesof the plurality of LEDs on the plurality of LED strings.
 17. A lampcomprising: a plurality of lighting strings, each lighting stringcomprising a plurality of light sources; a plurality of poweringcircuits for powering the plurality of lighting strings, wherein onepowering circuit is provided for each lighting string; a plurality ofshift registers for controlling the operation of the plurality ofpowering circuits, wherein at least one shift register is provided foreach lighting string; and a microprocessor for supplying timing pulsesto the plurality of shift registers for controlling operation of theplurality of powering circuits, the timing pulses comprising a pluralityof serial bit streams.
 18. A lamp according to claim 17 wherein thelight sources comprise LEDs.
 19. A lamp according to claim 17 whereinthe powering circuits comprise constant current circuits.